Finite Element Simulations of Flip Chip Solder Bumps with Fractures Present using FreeFem++

In this paper, 3D finite element models are built for flip chip solder bumps with fractures present. Three types of cracks are simulated with one located around the top interface of the bumps, one within the bulk and one around the bottom interface of the bumps. The mechanic equilibrium equations are solved to find the elastic stresses and thus to find the locations with stress concentration. Modal analyses are performed to find the influences of cracks on the natural frequencies of the bumps. Simulation results show that the stress concentration at the tip of a type II crack is much smaller; while evident stress concentration at the tips of both type I and III cracks are found except for the case of a type III crack with an applied shear stress; stress concentration is also found on the top surface of the Cu pad, and the maximum of Mises stress there varies on a small scale as the percentage of the fracture area increases; the percentage of the fracture area is not shown to have an evident influence on the natural frequency until the structure of the joint is sufficiently damaged by the crack.